Sensitivities of Mineral Dust Optical Properties to Surface Roughness

Mineral dust is the most abundant aerosol in the atmosphere and hence has a strong impact on atmospheric processes (i.e., aerosol-cloud and aerosol-radiation interactions). To learn more about the microphysical properties of mineral dust, remote sensing techniques using ground- and spaceborne lidars have been developed. These retrievals typically depend on fundamental assumptions about the shape and composition of the mineral dust particles. Since mineral dust particles are exclusively non-spherical, it is not appropriate to use spherical particles for the optical calculations. In the past, spheroids (Dubovik et al., 2006) and, more recently, the irregular hexahedra ensemble model (Saito et al., 2021) have been used as dust shape models. However, these models still neglect small-scale surface irregularity or surface roughness, an important morphological characteristic of mineral dust, which may lead to biases in retrieved microphysical properties.

We present preliminary results of a new dust morphological model, a roughened irregular hexahedra model. By using the random Fourier method, we add geometric surface roughness to the irregular hexahedra model particles, creating a more realistic-looking particle morphology than previously used models. We study the sensitivity of the optical properties to the degree of surface roughness. In particular, we focus on the impact on the integrated properties (i.e., single scattering albedo and asymmetry parameter), and the backscattering properties (i.e., the extinction-to-backscatter ratio and depolarization ratio), which are highly relevant for active remote sensing, and integrated (single scattering albedo and asymmetry parameter) properties. The new model shows promising results for better explaining lidar measurements. Furthermore, we present our plans for a flexible scattering database for use in remote sensing, radiative transfer, etc., openly available to the community.

O. Dubovik et al., “Application of spheroid models to account for aerosol particle nonsphericity in remote sensing of desert dust,” Journal of Geophysical Research: Atmospheres,2006

M. Saito, et al., “A Comprehensive Database of the Optical Properties of Irregular Aerosol Particles for Radiative Transfer Simulations,”2021